Compounding ingredients for unvulcanized rubber are often packaged by wrapping with thermoplastic film or placing in bags thereof. Polyethylene is sometimes used for such film because of its plasticity, antiblock property, relatively low cost, and because it can be obtained in a desirable melting temperature range so that the film will melt during the rubber mixing stage.
However, use of polyethylene is generally disadvantageous because, when mixed with unvulcanized rubber, it often does not disperse sufficiently in the matrix. This may leave minute areas within the matrix of the rubber when cured, which are themselves not cured and the resultant rubber may then contain some discontinuities.
Various solutions have been proposed and sometimes utilized. Very low softening point polyethylene has been used. Other thermoplastic materials and styrene/isobutylene based materials have been taught which may, optionally, also contain ingredients which they are used to package for rubber compounding purposes. (U.S. Pat. No. 2,617,775) Compounded elastomeric styrene/butadiene/styrene block copolymer films have been used with some success (U.S. Pat. Nos. 4,110,500 and 4,112,158) and (Canadian Pat. No. 794,200), but are somewhat more costly than polyethylene and sometimes do not provide an effective packaged article when its contents include quantities of oil of the rubber-processing type. Films of ethylene/vinyl acetate copolymer have been utilized. (U.S. Pat. Nos. 4,248,348, 4,334,615 and 4,378,067). Films of syndiotactic-1,2-polybutadiene have been taught, particularly as co-extruded films, as used for packaging compounding ingredients for rubber and the compounded rubber obtained thereby (U.S. Pat. No. 4,394,473).
In one aspect, this invention provides packaged materials for compounding rubber with a film and provides rubber compounded with such a package.